The present invention relates to a color display unit and, more particularly, to improvement in or relating to system for specifying a color of each portion of a picture to be displayed.
With conventional color display units, in the case of putting in colors to respective portions of a picture to be displayed, graphic forms corresponding to the colors are written by software into picture RAMs corresponding to the colors, taking into account the overlap of the graphic forms, and the outputs of the picture RAMs are combined to obtain video signals. For example, in the case where areas 1, 2 and 3 of a graphic form consisting of three overlapping circles are to be displayed in red, green and blue, respectively, as shown in FIG. 1A, a graphic form 5 of the area 1 to be colored in red, a graphic form 7 of the area 2 to be colored in green and a graphic form 9 of the area 3 to be colored in blue are written by software processing into red, green and blue picture RAMs 4, 6 and 8, respectively, as shown in FIGS. 1B to D.
For obtaining such graphic forms as shown in FIGS. 1B to D by finding their intersecting points through software processing, however, a lot of processing is needed, resulting in too much work being imposed on a microprocessor. Especially, when the graphic forms change their positions with time relative to one another, arithmetic processing must be executed for obtaining their intersecting points for each change, so that much time is consumed for the arithmetic processing, making it difficult, in practice, to provide such a colored graphic display.